In a University of North Texas study, guys who did just six total minutes of swings showed major boosts in their testosterone and growth hormone levels. And while this may not equal instant muscle, swings are still a one-stop shop for training because they work your entire body, including your abs, hamstrings and lats, says Dan John, the author of Mass Made Simple and a master kettlebell trainer. Do 30 seconds of kettlebell swings with a weight you can manage, then rest for 30 seconds. Repeat for 10 minutes.